The specific goal of the research study proposed for this fellowship is to investigate the feasibility, acceptability, and preliminary efficacy of a transdiagnostic, cognitive-behavioral therapy developed specifically to target common core processes across mood and anxiety disorders [Unified Protocol for Transdiagnostic Treatment of Emotional Disorders (UP)]1, for the treatment of patients with bipolar I disorder (BD-I) and comorbid anxiety. Conducting this project will provide the investigator with invaluable training in the successful implementation of clinical trials. The study will compare treatment-as-usual with pharmacotherapy (TAU) plus 18 one-hour sessions of treatment with the UP to TAU alone. Patients in both treatment conditions will be followed over a 12-month period and will be assessed monthly to track changes in mood, anxiety and emotion- related symptoms; functional impairment; and relapse rates. Data on the acceptability of the treatment will be gathered concurrently through monthly patient self-reported ratings of treatment satisfaction, and by tracking rates of acceptance for randomization into the study, number of completed sessions, and dropout rates. The study will examine: 1) whether combined cognitive behavioral treatment (UP) for BD-I and comorbid anxiety disorders is an acceptable and feasible approach to treatment; 2) whether treatment with the UP for BD-I and comorbid anxiety disorders as an adjunct to pharmacotherapy treatment-as-usual (TAU) leads to greater symptom reduction and reduced functional impairment than pharmacotherapy alone, 3) whether treatment for BD-I and comorbid anxiety disorders with the UP improves relapse rates over a 6-month follow-up relative to TAU; and 4) whether reduction in symptoms, relapse rates, and functional impairment are mediated by changes in emotion regulation skills. The broader aim of this study is to address the need for improved treatments for bipolar disorder. Bipolar disorder is a chronic and debilitating disorder, associated with significant personal and public health costs. Twelve-month adult prevalence rates of BD-I are 2.6%, with 83% classified as severe, and 48% utilizing health care services.2 Greater than 86% of BD-I patients have a lifetime diagnosis of comorbid anxiety.3 The presence of both current and lifetime comorbid anxiety has been identified as an independent marker of greater BD-I severity, and is associated with greater chronicity, reduced treatment response, and greater functional impairment.4,5 Therefore, treating anxiety in the context of BD-I is crucial for improving illness course and outcomes. Developing treatments for BD-I with comorbid anxiety is recognized as one of the greatest unmet needs in the field of bipolar disorder. The proposed project is intended to address this public health need, while simultaneously advancing and developing the applicant's training goals to become adept at conducting clinical trials.